In recent years, resistance change memories, including a resistive RAM (ReRAM) which uses variable resistive elements as memory elements and a phase-change RAM (PCRAM) which uses phase-change elements as memory elements, have been attracting attention as next-generation nonvolatile semiconductor memories.
The resistance change memories are characterized in that their memory cell arrays are of the cross point type, that they can achieve a very large memory capacity by three-dimensional integration, and that they can operate at as high a speed as a DRAM.
In a resistance change memory, a cross-point memory cell array is included a plurality of cell units. A cell unit is composed of a memory element and a non-ohmic element.
To improve the operating characteristic of a resistance change memory, an improvement in the characteristic of a non-ohmic element and the suppression of the deterioration of the characteristic of the element are required.
One factor that degrades the characteristic of a non-ohmic element is regarded to be the effect of electric resistance (interface resistance) developed at the interface between a semiconductor layer and a conducting layer which constitute the non-ohmic element.
Jpn. Pat. Appln. KOKAI Publication No. 2008-182121 has disclosed a configuration where a high-impurity-concentration n-type diffusion layer is stacked on an n-type diffusion layer in the cathode region of a bidirectional diode to decrease the contact resistance.